1. Field of the Invention
The present invention relates to a lithographic system and device manufacturing method for optimizing rasterization in maskless lithography.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern can be transferred onto all or part of the substrate (e.g., a glass plate), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate.
Instead of a circuit pattern, the patterning device can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can be a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A flat panel display substrate is typically rectangular in shape. Lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through a beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
Substrates used in a lithographic apparatus are typically of a standard size. The devices formed using a lithographic process, such as integrated circuit devices tend to be significantly smaller than the standard substrate. Accordingly, a plurality of devices of a given type are typically formed on each substrate. As will be appreciated, in mask-based lithography a cost saving can be realized by using a single mask to repeatedly expose the same pattern on a plurality of different areas on the substrate. The mask, for example, provides the pattern necessary to form a layer of a single device or can provide the pattern for a layer of several adjacent devices, depending on the size of the device to be formed relative to the size of the exposure field of the lithographic apparatus. The lithographic apparatus can be arranged such that it can be used with masks of different sizes in order to accommodate conveniently the manufacture of devices of different sizes.
In a maskless lithographic apparatus, e.g., one using a programmable patterning device rather than a mask, the apparatus is inherently capable of being used for the manufacture of devices of any size (up to the size of the substrate) and, indeed, can be used to manufacture a plurality of different devices on a single substrate because the programmable patterning device can be set to provide any required pattern. However, the data processing architecture required to convert a desired pattern into the necessary control signals for a programmable patterning device is a significant portion of the cost of a maskless lithographic apparatus. Accordingly, it is desirable to minimize the cost of the data processing architecture where possible.
Therefore, what is needed is a system and method in which the cost of a data processing architecture used to provide control signals for a programmable patterning device can be reduced.